Scientist Greg Asner peers out a window during a flight to map tree health in the Sierra Nevada.

Scientist Greg Asner peers out a window during a flight to map tree health in the Sierra Nevada.

Photo: Max Whittaker/Prime, Special To The Chronicle

Image 3 of 6

Scientist Greg Asner mounts a GoPro camera on the Carnegie Airborne Observatory before a flight to map tree health in the Sierras in McClellan Park, California, July 27, 2016.

Scientist Greg Asner mounts a GoPro camera on the Carnegie Airborne Observatory before a flight to map tree health in the Sierras in McClellan Park, California, July 27, 2016.

Photo: Max Whittaker/Prime, Special To The Chronicle

Image 4 of 6

Asner monitors software during a flight to map the spread of dying trees in the Sierra Nevada. He expects the death toll to rise by tens of millions, even if heavier rains come this year.

Asner monitors software during a flight to map the spread of dying trees in the Sierra Nevada. He expects the death toll to rise by tens of millions, even if heavier rains come this year.

Photo: Max Whittaker/Prime, Special To The Chronicle

Image 5 of 6

An imaging spectrometer sits in the back of the Carnegie Airborne Observatory with a portrait of Andrew Carnegie on the door in McClellan Park.

An imaging spectrometer sits in the back of the Carnegie Airborne Observatory with a portrait of Andrew Carnegie on the door in McClellan Park.

Photo: Max Whittaker/Prime, Special To The Chronicle

Image 6 of 6

The Carnegie Airborne Observatory, a Dornier 228, stops to refuel in Bakersfield during trip to assess tree health and map dying forests in California.

The Carnegie Airborne Observatory, a Dornier 228, stops to refuel in Bakersfield during trip to assess tree health and map dying forests in California.

Photo: Max Whittaker/Prime, Special To The Chronicle

An eye-opening flight over California’s dying forests

1 / 6

Back to Gallery

McCLELLAN PARK, Sacramento County — Even before the plane left the runway, it was clear the crew of researchers examining the fallout from California’s historic drought would not return with good news.

A column of gray smoke from a smoldering brush fire was visible from McClellan Airfield outside Sacramento, a reminder of the threat that the hot, dry weather posed for the state’s forests — the subject of the high-flying mission.

The four crew members were halfway through two weeks of flights over landscapes shifting ominously from green to brown, and already they’d begun to draw their conclusion: The mind-boggling number of trees that have died in California due to drought — an estimated 66 million over five years — is only the beginning.

The death toll will probably rise by tens of millions of trees, even if heavier rains come this year, said Greg Asner, head of the team from Carnegie Institution for Science in Washington, D.C.

Using technology that has diagnosed problems in the Amazon rain forest and the jungles of Borneo, the researchers are learning that California’s unprecedented tree die-off is moving well beyond its origins in the southern Sierra Nevada and along parts of the southern coast. It’s creeping farther north, and to higher elevations, not only providing tinder for wildfires, but also obstructing the forests’ fundamental ability to provide clean water and absorb carbon dioxide.

“It’s not just the numbers of trees lost. … It’s the implications,” said Asner, who works out of Stanford University when he’s not in the air. “The scientist in me is quite happy that we have a predictive capability, but the human in me and the naturalist in me is quite shocked.”

Flight over California's dying forests

Media: kalexander@sfchronicle.com / San Francisco Chronicle

On this particular day, late last month, the plan was to jet south from Sacramento to ground zero of the epidemic, then turn and head north, where the flyover would yield a clearer picture of just how high and far the problem extends.

“You’re not really seeing anything yet,” said Asner, as he peered out the window at a splash of amber in an otherwise green canopy of trees shortly after takeoff. “Wait until we get farther along.”

Flying in the Carnegie Institution’s 54-foot, custom-built, twin-turboprop plane can be unnerving.

It’s not that the scientific instruments take up so much room that there’s no bathroom, requiring six hours of discipline on the part of crew members. And it’s not the turbulence, because the ride is surprisingly smooth, much like a small commercial aircraft. A sign in the cockpit reads, “No acrobatic maneuvers, including spins, approved.”

What’s daunting is the remarkable ability of the plane to collect data on nearly every tree it flies over — from 7,700 feet above — and use the information to foretell the grim future of the forest.

Aboard the Carnegie Airborne Observatory is a one-of-a-kind imaging spectrometer that uses sunlight to measure the molecular composition of trees. By determining water content, the researchers can pinpoint which trees are becoming too dry to survive, even when they may appear perfectly healthy.

Photo: Max Whittaker/Prime, Special To The Chronicle

Greg Asner of the Carnegie Institution for Science, above, assesses dead and dying trees in the southern Sierra, top, during a flight to map the health of trees.

Greg Asner of the Carnegie Institution for Science, above, assesses...

“Even though it looks green to the naked eye … those trees are departed, they’re gone,” said Asner. “You’re in the presence of technology that many people don’t think exists.”

The crew’s forecasts have proved extraordinarily accurate. Last year, when the team flew a similar mission in California, the researchers identified 58 million trees that were dead or close to dying, just shy of the 66 million casualties cited in a U.S. Forest Service count released this summer.

“I was told by a lot of people that it wouldn’t ever spread as far,” said Asner, as he mapped the die-off on his onboard computer with crewmate Joseph Heckler. “But look what we’re flying over. Most of this was all fine last year.”

As the aircraft pushed to the southern Sierra, not far from Fresno, clover-green hillsides gave way to sprawling patches of yellow, orange and cinnamon. High-elevation lakes, like Shaver Lake in Fresno County and Bass Lake in Madera County, were almost completely surrounded by dead trees. Wooded canyons in Sequoia and Kings Canyon national parks appeared rust-colored. Mountains east of Bakersfield were bronze.

Photo: Max Whittaker/Prime, Special To The Chronicle

Dead trees dot the landscape of the Sierra just south of Yosemite. The number of dying trees in the state is creeping northward.

Dead trees dot the landscape of the Sierra just south of Yosemite....

The plane veered toward the coast, flying over the Los Padres National Forest near Santa Barbara. It was more of the same.

On this particular afternoon, the skies were unusually smoky above Southern California. Airspace had been closed near Los Angeles to accommodate planes doing battle with a 41,000-acre blaze north of the city. The Carnegie Airborne Observatory was forced to make a slight change to its flight plan.

The potential for catastrophic wildfire, Asner said, is the most immediate danger presented by dying trees.

The U.S. Forest Service and the California Department of Forestry and Fire Protection, which fight the bulk of the state’s wildfires, are helping fund the Carnegie Institution’s flights, along with the National Park Service and David and Lucile Packard Foundation.

“Prediction will give the agencies a chance to be less reactive,” said Asner, noting the ability of fire officials to start prescribed burns and forest thinning in more vulnerable areas.

But the repercussions of the tree die-off don’t end with fire.

Rivers and lakes whose water is naturally filtered by forests are likely to become more degraded as trees perish, potentially hurting water supplies. Meanwhile, the carbon stored in trees is released into the atmosphere when they die, contributing to the buildup of greenhouse gases and global warming.

Ultimately, the magnitude of tree mortality may signal a wholesale transformation of the forest. Some scientists speculate that woodlands, in many areas, will disappear and give way to brush and grasses that are more tolerant of hotter, dryer weather.

Noah Diffenbaugh, a climate expert who works with Asner at Stanford, sees the drought as the beginning of a future full of similarly arid periods, which could reshuffle the geography of plants and animals.

“There’s mountains of evidence that climate shifts have led to changes in ecosystems,” Diffenbaugh said.

As the plane curled back toward the Sierra, Asner wondered aloud whether the forests had already begun to radically change.

The die-off that started with mostly ponderosa pine at roughly 6,000 feet, along with cedar and oaks, is moving to trees at higher elevations such as sugar pine and red and white fir. Little of the forest appears immune, he said.

“Is it a drought or is it a mega-shift?” Asner asked.

The trees are not only compromised by thirst, but also a lack of strength to fend off beetle attacks, which are responsible for a great deal of the deaths. The trees are several years short of water, according to the researchers, so dry that they need the nourishment of at least two or three wet years to begin reversing the decline.

The latest species experiencing problems is the western white pine. The crew recently found stands of those trees as high as 8,000 feet struggling.

Before the plane climbed to survey a tall mountain pass, pilots Don Koopmans and Devon Woodward slipped on their oxygen masks.

“I don’t know if those trees are going to die,” said Asner, having recorded the water content of a number of white pines. “But they’re stressed.”

One of the few trees that remains unaffected by drought is the giant sequoia. The titans of the forest can live 3,000 years, and they’ve seen plenty of dry periods before.

While few parts of California have escaped the die-off, the vast tracts of dead trees visible in the southern Sierra are not as prevalent to the north. The Bay Area, for example, has seen relatively little damage.

Still, as the plane sped along the western edge of Yosemite National Park, back to McClellan Airfield, Asner pointed to several brown areas.

“What we’re seeing is a movement of the wave of tree mortality up north as you go up the Sierras,” he said.

Asner’s crew recently found swaths of lifeless trees around Lake Tahoe, and the water measurements suggest more will emerge. Even trees near Mount Shasta and along the northern coast are dying, though in smaller numbers.

Asner anticipates his research will show the impact of the drought and beetle infestation to be double what it was last year — not necessarily twice as many dead trees, he said, but twice as much stress on forests. The extent of the problem will be detailed in a paper that Asner plans to write after the flights, which concluded Friday.

The Drought

“The spreading of dead trees has been much faster than I thought would happen,” he said, before the plane began its final descent.

By the end of the day, news emerged that the state’s budding wildfire season — fueled by dying trees — had claimed its seventh life when a bulldozer overturned in a firefight along the Big Sur coast.

Gov. Jerry Brown has streamlined funding to remove dead and fire-prone trees under an emergency order issued last year. But the few hundred thousand that have been felled so far will have limited benefit. The cutting isn’t likely to keep up with the die-off.

“If it doesn’t rain or snow, it will just keep going,” Asner said. “I’m not optimistic.”